My 2006 Pontiac g6 SE 2.4l that I'm buying from a buddy of mine and it has almost 98k miles on it and when you turn the key the guages in the cluster swing which I think is normal because of the sensors checking the systems in the car but I look at my odometer and it says 0 miles at first but after about 3 seconds of having the key in the run position it goes on to say error but when I had the spare key (non transponder) it read 98k but sometimes said error. When I go to start the car though besides a bad battery the car cranks right up but runs really rich. I ran through a quarter tank of gas just by letting it idle for 20 mins. And it only gets about 11mpg. But I can't read any codes from the check engine light because the obd2 port isn't getting any power and I checked all fuses and cleanliness of the port. And my speed sensor went out on the car and the car wont shift and when i throw it in reverse my reverse lights won't kick on. Can someone help me out with making me 100% positive that it's just my pcm and speed sensor that's bad?